1. Technical Field
The invention relates to vehicle axles and wheel end assemblies, and in particular to axles and wheel end assemblies for heavy-duty vehicles, such as tractor-trailers. More particularly, the invention is directed to a heavy-duty axle spindle and wheel end assembly that are capable of selectively accommodating a conventional dual-wheel, standard-tire configuration and a single-wheel, wide-tire configuration in a robust, yet economical and lightweight manner.
2. Background Art
For many year's, the heavy-duty vehicle industry has utilized wheel end assemblies which typically are mounted on each end of one or more non-drive axles. Each wheel end assembly typically includes a hub rotatably mounted on a bearing assembly that in turn is immovably mounted on the outboard end of the axle, commonly known as an axle spindle. As is well known to those skilled in the art, for normal operation of the wheel end assembly to occur, the bearing assembly and surrounding components must be lubricated with grease or oil. Therefore, the wheel end assembly must be sealed to prevent leakage of the lubricant, and also to prevent contaminants from entering the assembly, both of which could be detrimental to its performance. More specifically, a hubcap is mounted on an outboard end of the wheel hub, and a main seal is rotatably mounted on an inboard end of the hub and the bearing assembly in abutment with the axle spindle, resulting in a closed or sealed wheel end assembly.
While most wheel end assemblies include these general features, the design and arrangement of the hub, bearing assembly, hubcap, main seal, and other components, as well as the axle spindle, vary according to the specific vehicle design and its anticipated uses. For example, some heavy-duty vehicles include axle spindles and wheel end assemblies designed for a dual-wheel, standard-tire configuration in which two wheels, each having a respective tire mounted thereon, are mounted on a single hub.
In a dual-wheel, standard-tire configuration, the focus of the load forces acting on the axle spindle and the wheel end assembly during operation of the vehicle, typically referred to in the art as the load line, acts on a plane that extends generally vertically through the axle spindle and the wheel end assembly at a point between the two wheels. Such a load line is located further inboard than load lines of other wheel configurations, to be discussed below, thus creating a shorter moment arm than that created by other wheel configurations. A shorter moment arm in turn creates less loading on the components of the axle spindle and the wheel end assembly than a wheel configuration that has a load line which is further outboard and thus a longer moment aim. As a result, the hub, bearing assembly and axle spindle for a dual-wheel, standard-tire configuration typically are of a comparatively less robust construction than the hub, bearing assembly and axle spindle used with types of wheel configurations that have a load line which is further outboard. This less robust construction enables the axle spindle and wheel end assembly to be comparatively lightweight and economical for dual-wheel, standard-tire configurations, which is desirable in the heavy-duty vehicle industry.
Due to common wheel attachment interfaces, such a less robust axle spindle and wheel end assembly construction may also selectively accommodate a single-wheel, wide-tire configuration, in which one wheel with a single wide tire mounted thereon is in turn mounted on the hub. This single wide tire is a high weight capacity and high speed capacity tire that is intended to replace a dual-wheel, standard-tire configuration. However, the less robust construction of the axle spindle and the wheel end assembly limits the range of single-wheel, wide-tire types to ones having only a zero offset or a near-zero offset, such as an 0.56-inch offset, to keep the load line in a location that is similar to that of the above-described dual-wheel, standard-tire configuration. Any other type of single-wheel, wide-tire configuration moves the load line further outboard, and thus places an increased load on the outboard beating of the bearing assembly, which causes that beating to experience increased fatigue loading and significantly reduces its useful life.
More particularly, a zero-offset wheel is one in which the vertical centerline of the wheel is generally aligned with the mounting surface of the hub or brake drum, which reduces the operational load forces on the axle spindle and the wheel end assembly, and on the outboard beating in particular. However, a single-wheel, wide-tire with a zero offset has a narrower wheel base than a dual-wheel, wide tire configuration, which creates certain disadvantages when it is desired to change from one type of wheel configuration to another on a heavy-duty vehicle, such as a semi-trailer. For example, if it is desired to change from a dual-wheel, standard-tire configuration to a single-wheel, wide-tire configuration and maintain roll stability of the vehicle, the frame, subframe, axle and/or suspension assemblies of the semi-trailer must be modified to move the wheels further apart and widen the wheel base. In addition, if it is desired to return to a dual-wheel, standard-tire configuration after such modifications for a zero-offset, single-wheel, wide-tire configuration, additional modifications must be performed to move the wheels closer together, so the tires do not extend outboardly past the body of the vehicle and exceed legal restrictions on the width of a heavy-duty vehicle. The time and expense for such modifications associated with roll stability thereby reduce the desirability of a zero-offset single-wheel, wide-tire configuration for a less robust axle spindle and wheel end assembly.
In contrast, axle spindles and wheel end assemblies that are of a more robust construction are able to selectively accommodate a wider range of single-wheel, wide-tire configurations, including wheels having a two-inch offset, as well as a dual-wheel, standard-tire configuration. A two-inch offset wheel is one in which the vertical centerline of the wheel is located about two inches outboard of the mounting surface of the hub or brake drum, which creates increased operational load forces. That is, the load line acts on a vertical plane that is further outboard than the load line associated with a dual-wheel, standard-tire configuration or a zero-offset, single-wheel configuration. Since the load line of the two-inch offset wheel configuration is further outboard, a greater moment arm is created, leading to increased loading on the components of the axle spindle and the wheel end assembly. Such increased loading creates the need for the more robust construction of the wheel end assembly, including the hub and bearing assembly, especially the outboard bearing of the bearing assembly, as well as the axle spindle, to obtain acceptable bearing and spindle life.
As mentioned above, the axle spindles and wheel end assemblies of more robust construction also are able to accommodate a dual-wheel, standard-tire configuration. To this end, when a heavy-duty vehicle such as a semi-trailer uses a single-wheel, wide-tire configuration, the advantage of the two-inch offset wheel is that such wheels generally include a relatively wide wheel base that is roll stable. As a result, modifications of the frame, subframe, axle and/or suspension assemblies are not necessary when it is desired to change from a dual-wheel, standard-tire configuration to a single-wheel, wide-tire configuration, or back to a dual-wheel, standard-tire configuration. However, the disadvantage of such more robust axle spindles and wheel end assemblies is that they are typically relatively heavy and/or expensive, and are not optimized for the different load line conditions of a dual-wheel, standard tire configuration and a single-wheel, wide tire configuration, which are undesirable characteristics.
The capability of certain heavy-duty vehicles to selectively accommodate a dual-wheel, standard-tire configuration and a single-wheel, two-inch offset wide-tire configuration is becoming increasingly important in the heavy-duty vehicle industry. For example, it is becoming more common for the owner of a fleet of heavy-duty vehicles to use a single-wheel, two-inch offset wide-tire configuration on his/her vehicles, since such a wheel configuration is associated in the industry with high performance, lower weight, and fuel savings. However, when the owner sells the vehicles, the owner will convert them to a dual-wheel, standard-tire configuration to make them more attractive in the used vehicle market. In order to obtain the legal maximum axle rating for a single-wheel, two-inch offset wide-tire configuration, which by way of example is 20,000 pounds, and for a dual-wheel, standard-tire configuration, which by way of example is 23,000 pounds, an axle spindle and wheel end assembly of more robust construction must be used, as described above. However, the increased weight and/or cost associated with the more robust axle spindle and wheel end assembly are undesirable.
Moreover, the bearing assembly of a prior art wheel end assembly typically includes an inboard bearing and an outboard bearing. In certain wheel end assembly configurations, a bearing spacer extends between the inboard and outboard bearings. Many bearing spacers have a relatively significant length, which may be due to various factors, such as the length of the axle spindle. Such a significant length for a bearing spacer can increase the difficulty of maintaining a precise, repeatable length-related tolerance during manufacture, thereby possibly undesirably reducing the life of the main seal and/or the fatigue life of the bearings. More particularly, the bearing spacer sets a specific gap between the bearings, so that a specific preload of the bearing cones and bearing spacer is achieved once the wheel end assembly is property assembled on the axle spindle. When the bearing spacer is relatively long it has a greater variance in its length than a shorter bearing spacer, since the length-related dimensional tolerance of a spacer generally increases as the desired length of the spacer increases. Thus, for a long bearing spacer, it is difficult to maintain a precise, repeatable length-related tolerance.
When a precise, repeatable length-related tolerance is not maintained, the bearing spacer may be longer than a desired length, which may allow excessive axial end play of the wheel end assembly relative to the axle spindle, which in turn may allow excessive movement of the main seal, possibly reducing the life of the main seal. Alternatively, the bearing spacer may be shorter than a desired length, which may create an overloading of the bearings when the wheel end assembly is assembled on the axle spindle, which in turn may reduce the fatigue life of the bearings.
These disadvantages of prior art axle spindles and wheel end assemblies make it desirable to develop an axle spindle and a wheel end assembly that are capable of selectively accommodating a dual-wheel, standard-tire configuration and a single-wheel, two-inch offset wide-tire configuration in a relatively economical and lightweight manner, and which facilitate the optional use of a bearing spacer that provides an improved repeatable length-related tolerance. The present invention satisfies these needs.